What bride would leave thier sister in law of 15 years out of thier wedding?

My sister in law has asked my husband and two kids to stand in her wedding and not me. I feel so left out of the family. We are a small family it's just us and her mom, they are all going out to buy dresses and clothes while I just stand there and watch. I'm starting to get really upset, and hurt. She asked me to hold purses while her bridesmaids rehearsed. She's my kids godmother, and we get along so well. Maybe she just doesn't realize, she is hurting my feeling. My husband told her how I felt and she said there was no place for me in the wedding. My husband and son walked her down the aisle and my daughter is her flower girl. I'm getting so upset, I don't even want to go to the wedding, or if I do I will be there for my family and not her.